Hot water solar heating system and method

ABSTRACT

A solar hot water system includes a mirror which reflects solar energy on an absorber including a water pipe and two plates to heat water in the pipe. When water in the pipe freezes and expands, the pipe and the plates are elastically deformed without injury.

FIELD OF THE DISCLOSURE

The disclosure relates to a system for solar heating hot water and to amethod for operating a solar heating system.

BACKGROUND OF THE DISCLOSURE

Solar heating systems for heating water and flowing the heated water toa hot water tank are well known. Water from a tank inside a building isflowed through a supply pipe to a solar collector assembly locatedoutside the building, is heated by solar energy and is flowed through areturn pipe back into the building and to the tank. In its simplestform, the solar collector assembly includes a solar collector having anabsorber which heats a pipe carrying water from the tank. A circulationpump flows water from the tank to the collector assembly and back to thetank.

A solar heating system of this type can operate even when the outdoortemperature is below freezing. This is because collected solar energycan heat the pipe in the collector assembly to a temperaturesufficiently high to heat water in the tank. However, the supply andreturn pipes may be exposed to outdoor temperature below freezing sothat water in these pipes freezes, blocks flow and prevents operation ofthe heating system.

During cloudy days or at nighttime, the temperature inside the solarcollector assembly may fall below freezing with the result that water inthe water pipe in the solar collector freezes and expands. This cancause the pipe to become irreversibly deformed or to rupture.

Conventional solar heating systems for use in locations where freezingtemperatures occur avoid the problem of frozen supply and return pipesand frozen water pipes in solar collectors by draining the water fromthe pipes when solar radiation is absent or insufficient to provideheating. This increases system complexity and prevents use of the systemduring cold months.

Another solution to the problem of frozen pipes in solar heating systemsis to eliminate tank water from the pipes and substitute a non-freezingliquid, such as an ethylene glycol-water mixture. The mixture iscirculated through the solar collector, is heated by solar energy and isthen flowed to a heat exchanger external of the water tank. Heat fromthe ethylene glycol mixture is flowed to water in the exchanger, whichis heated and then flowed to the tank. This solution is less efficientthan a system in which tank water is heated directly in the solarcollector assembly and is considerably more complicated and expensivethan a system using water as a heat transfer medium.

Accordingly, there is a need for an improved solar heating system with asolar collector assembly using a solar collector with a water pipe wherefreezing of water in the solar collector pipe does not cause damage.

There is also need for a system which automatically clears an iceblockage in a supply or return pipe and resumes operation after an iceblockage has been cleared. The system should have a solar collectorusing a water heating pipe which is not damaged when water in the pipefreezes and expands.

SUMMARY OF THE DISCLOSURE

The hot water solar heating system according to the disclosure has asolar collector assembly mounted on the outside of a building and a hotwater tank inside the building. Water from the tank is flowed through asupply pipe to a non-circular water heating pipe in the solar collectorassembly and through a return pipe back to the tank. Portions of thesupply and return pipes are located outside the building. An iceblockage in the water heating pipe in the collector assembly elasticallyexpands the pipe and elastically deforms the solar absorber contactingthe pipe without impairing the heat flow connection between the absorberand the pipe or causing leaks. The pipe and portion of the absorbercontacting the pipe are elastically flexed outwardly together. When thewater in the pipe melts, the pipe and the portions of the assembly incontact with the pipe elastically return to their original shape. Nodamage is caused by expansion of frozen water in the pipe.

The water heating pipe has a non-circular cross section and is formedfrom an elastically deformable metal, which may be austenitic stainlesssteel. The cross section pipe may be oval or elongate with generallyparallel sides. The energy absorbing plates in the solar collectorcontact the sides of the heating pipe for heat transfer to heat water inthe pipe. Expansion of water in the heating pipe as it freezes into iceto form a blockage elastically deforms the pipe and the absorbing plateoutwardly but does not permanently deform or damage them. When solarenergy melts the blockage, the pipe and collector elastically return totheir initial shapes.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representational view of a first embodiment solar heatingsystem according to the disclosure;

FIG. 2 is a perspective view of a first solar collector;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2;

FIG. 4 is an enlarged sectional view of an absorber and water heatingpipe shown in FIG. 3.

FIG. 5 is a sectional view along line 5-5 of FIG. 1;

FIG. 6 is a representational view of a second embodiment solar heatingsystem;

FIG. 7 is a representational view of a third embodiment solar heatingsystem;

FIG. 8 is a representational view of a fourth embodiment solar heatingsystem;

FIG. 9 is a transverse sectional view through a second solar collector;

FIG. 10 is a partially broken away transverse sectional view through thesolar collector of FIG. 9 when the water in the water heating pipe isliquid; and

FIG. 11 is a view like FIG. 10 when the water in the water heating pipeis frozen and has expanded.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Solar heating system 10 is illustrated in FIG. 1. System 10 includes asolar collector assembly 12, and a heated water storage tank 14. Thesystem provides heated water for use in a building, typically aresidential dwelling. The solar collector assembly 12 is mounted on theoutside of the building and is positioned to receive solar energy. Thetank 14 is located inside the building.

Cold water supply pipe 16 flows water to the bottom of tank 14 from awater source. Heated water outflow pipe 18 flows heated water from thetop of the tank for use in the building. Collector supply pipe 20extends from the bottom of tank 14 to collector assembly 12. Collectorreturn pipe 22 extends from the collector assembly to the top of thetank. Pipes 20 and 22 are formed preferably from PEX tubing. Circulatorpump 26 located in pipe 20 flows water from the bottom of the tankthrough pipe 20, assembly 12 and pipe 22 back to the top of the tank.Water flowed through assembly 12 is heated by solar energy and heats thewater in the tank. The portions 28 and 30 of pipes 20 and 22 outside ofbuilding wall 54 are connected to water heating pipe 56 running throughcollector assembly 12. Pipes 20, 56 and 22 form water conduit 24extending from the tank 14, to assembly 12 and back to the tank.

Supply and return pipes 20 and 22 extend from tank 14 inside thebuilding, through the exterior building wall 54 to collector assembly 12mounted on the exterior of the building, typically on the roof of thebuilding. The outdoor portions 28 and 30 of pipes 20 and 22 run fromwall 54 to assembly 12. Portions 28 and 30 may extend from ground levelup along a side of the building to assembly 12 mounted on the roof ofthe building. Pipes 20 and 22 are surrounded by tubes of thermalinsulation 32 and outer protective sheaths 34. See FIG. 5. Theinsulation 32 minimizes thermal losses in pipes 20 and 22 and preventscondensation. Pipes 20 and 22 are typically formed from PEX tubing whichis not injured by freezing of water within it.

Electric control circuit 36 operates system 10. Circuit 36 is connectedto flow sensor 38 located in collector supply pipe 20, and todifferential thermostat 40. Circuit 36 activates and deactivates anelectric resistance heating wire 42 located in each outdoor portion 28and 30 of pipes 20 and 22.

Thermostat 40 includes temperature sensor 44 in tank 14 and temperaturesensor 46 on water heating pipe 56 in collector assembly 12. Sensor 44senses the temperature of the water in the tank. Sensor 46 senses thetemperature of the water in pipe 56 in the collector assembly. Thedifferential thermostat 40 senses when the temperature at the heatingpipe 56 exceeds the temperature of water in tank 14 by a predeterminedamount using inputs from sensors 44 and 46, and when this conditionexists it sends a signal to control circuit 36.

Power wire 48 extends from control circuit 36 through the wall of pipe20 inside of building wall 54 and is connected to a resistance heatingwire 42 in pipe portion 28 extending from wall 54 to housing 60.

Power wire 50 extends from the end of the resistance heating wire 42 inpipe 20 adjacent the housing 60, through the wall of the pipe, along thehousing, through the wall of pipe 22 adjacent housing 60 and joins theend of a second resistance heating wire 42 in the outer end 30 of pipe22. Wire 42 extends along the interior of pipe 22 through wall 54 andinside the building. Power wire 52 extends from the end of wire 42through the wall of pipe 22 and to control circuit 36. When actuated,the two resistance heating wires 42 melt ice blockages in the exteriorportions 28 and 30 of pipes 20 and 22 extending from wall 54 tocollector assembly 12. Alternatively, the power wires 48 and 50 may belengths of double conductor wires with the wires joined at ends of thepower wires and with the two lengths extending through the pipes atsingle locations in the pipes.

Solar collector assembly 12 includes four solar collectors 58 mountedside-by-side in housing 60. A sheet transparent to solar energy overliesthe top of the housing to provide thermal insulation and to preventwater and debris from entering the housing. If desired, solar collectors144, disclosed in FIGS. 9-11, may be used in place of solar collectors58.

Each solar collector 58 includes an elongate, semi-cylindrical mirror 62and a vertical solar absorber 64 in the center of the mirror. Waterheating pipe 56 extends along the center of the absorber 64 between apair of like energy absorber plates 66.

The pipe 56 is elliptical in cross section and has a short axis 70 and along axis 68. The pipe is preferably formed from thin walled, elasticmetal which may be austenitic or Series 300 stainless steel. The pipesidewall may be about 0.020 inches thick to permit elastic outwardflexing of the sidewall of the pipe when water in the pipe freezes andincreases in volume. The pipe short axis 70 is sufficiently less thanits long axis 68 so that when water in the pipe freezes and expandsabout 9%, the increased volume of the ice in the pipe elasticallyexpands the pipe but does not expand the pipe to a maximum, circularcross section. Expansion of the pipe does not permanently deform orcrack the pipe. When ice in the pipe melts, the pipe elastically returnsto its original shape.

Elliptical pipe 56 should have an axis ratio (length of long axis 68divided by length of short axis 70) of 1.44 or greater to prevent freezeexpansion of the pipe to a circular cross section. In practice, the pipemay have an axis ratio of at least 1.50 to limit flexing of the pipewhen water freezes and to reduce the possibility of fatigue cracking.

Pipe 56 need not have an elliptical cross section. The pipe may have twoopposed long sides joined by short ends, or other cross sectional shapeswhich permit outward elastic flexing of the pipe wall when water in thepipe freezes. Typical domestic water pressure of less than 100 psi doesnot significantly deform pipe 56.

Energy absorbing plates 66 are preferably formed from extrusions of highthermal conductivity metal, such as aluminum. Each plate includes aflat, two-sided absorber panel 72 extending away from pipe 56 in adirection along pipe long axis 68. A pair of opposed solar energytransfer arms 74 at the inner edge of panel 72 extend to either side ofpipe 56. The arms 74 are connected to the panels 72 by beams 80. Theconcave inner surfaces 76 of arms 74 are semi-elliptical in shape andare in surface-to-surface heat transfer contact with the outer surfaceof pipe 56. See FIG. 4. A slot or slit 78 extends from arms 74 intopanel 72 to either side of beams 80 to permit elastic flexing of thebeams and outward movement of arms 74 with expansion of pipe 56 whenwater in the pipe freezes.

The spacing between arms 74 before mounting of plates 66 on the pipe 56is slightly less than shown in FIG. 4 so that beams 80 are flexedoutwardly slightly when the plates are mounted on the pipe and tight,surface-to-surface heat transfer connections are established betweenarms 74 and pipe 56. The connections promote efficient flow of solarheat from the plates to the pipe to heat water in the pipe.

If desired, a thin layer of flexible, thermally conductive material canbe provided in the interface between surfaces 76 of arms 74 and theouter surface of pipe 56. The flexible, thermally conductive materialmay be silicon grease with thermally conductive particles. The materialincreases heat flow from the plates 66 to the pipe.

Water heating pipe 56 includes an inlet end 82 joined to pipe 20 and anoutlet end 84 joined to pipe 22. The pipe 56 includes four straightheat-absorbing lengths 86 each extending along one of the fourside-by-side semi-cylindrical mirrors 62 in assembly 12. The pipe alsoincludes three semi-circular, 180-degree bends 88 between adjacent pipelengths 86. Mirrors 62 may have a diameter of eight inches so that theradius of curvature of bends 88 is four inches.

Pipe 56 may be formed from a continuous length of elliptical stainlesssteel piping. Tooling is used to bend segments of the pipe about axesparallel to the pipe long axis 68 to form bends 88. Forming bends 88 bybending elliptical pipe around its long axis is easier than formingbends in a cylindrical pipe or bending elliptical pipe around an axisparallel to the short pipe axis.

Portions 28 and 30 of pipes 20 and 22 extend outside of the building andare exposed to temperatures which can form ice blockages in the PEXtubing. An ice blockage prevents flow of water through system 10 butdoes not injure the PEX tubing. Resistance heating wires 42 extendthrough the interiors of portions 28 and 30 of pipes 20 and 22 and arein direct contact with any ice blockage in the outdoor portions of thepipes. Heating of the resistance wires efficiently melts the iceblockage.

If desired, a resistance heating wire, or a number of resistance heatingwires, may be mounted outside pipe portions 28 and 30. Flowingelectricity through a wire or wires mounted on the outside of theportions heats each pipe and melts an ice blockage in the pipe.

The semi-cylindrical mirrors 62 have highly reflective inner surfaces.Sunlight received by the mirrors is reflected inwardly against thevertical absorber 64. The sides of absorber plates 66 haveheat-absorbing coatings to absorb heat from light reflected against theplates by the mirrors. Sunlight received by the mirrors is reflectedagainst the absorber plates, independent of the angle at which the lightstrikes the mirrors.

Mirrors 62 need not be semi-cylindrical. The mirrors may have differentshapes in order to reflect captured light onto plates 66.

The operation of solar heating system 10 will now be described.

Sunlight is reflected by mirrors 62 against both sides of absorbers 64to heat plates 66. Heat from the plates flows to pipe 56 to heat waterin the pipe. When the temperature in pipe 56, as determined by sensor46, exceeds the temperature of the water in tank 14, as determined bysensor 44, by a predetermined difference, which may be 30 degrees F.,the differential thermostat 40 sends a signal to control circuit 36 andthe circuit actuates circulator pump 26. Pump 26 flows water from thebottom of tank 14 through the collector assembly 12 for solar heatingand flows the heated water from the assembly into the top of the tank toheat the tank water. When the temperature of the water in the collectorassembly no longer exceeds the temperature of the water in the tank bythe predetermined difference, the control circuit 36 turns offcirculator pump 26.

If the temperature outside the building wall 54 falls below freezing,water in the outside portions 28 and 30 of pipes 20 and 22 may freeze,despite the fact that water in pipe 56 in collector assembly 12 isheated above freezing and may be warmer than water in tank 14. In thisevent, an ice blockage prevents solar heating of water in tank 14.

When water freezes to block pipe portion 28 or 30, pump 26 will run butwater will not flow through pipe 20, pipe 56 and pipe 22. The absence offlow while pump 26 is running is detected by direct flow sensor 38 whichsends a signal to circuit 36. Circuit 36 then flows electricity throughpower wires 48 and 52 to heat the resistance wires 42 in pipe portions28 and 30. One of the wires 42 extends past the ice blockage. Heat fromthe wire 42 melts the ice blockage to reestablish flow of water throughthe pipe 56 by pump 26.

The resistance heating wires 42 are activated until sensor 38 detectsreestablished flow of water, which may be slight at first. Once flow hasbeen reestablished, a signal from flow sensor 38 actuates circuit 36 todeactivate the wires 42. Water is flowed past the remaining ice torapidly melt the ice and reestablish normal operation of system 10,despite an outdoor temperature below freezing.

Flow sensor 38 detects decreased flow or no flow due to an ice blockage.The sensor may include a vane or a rotary turbine wheel located insupply pipe 20 and a detector responsive to movement of the vane orwheel. Other types of flow sensors may be used if desired includingdifferential pressure flow sensors, ultrasonic flow sensors,calorimetric flow sensors, and the like.

FIG. 6 illustrates a second embodiment solar heating system 90 which islike solar heating system 10. Reference numbers shown in FIG. 5, whichare identical to reference numbers shown in FIG. 1, describe componentsof system 90 identical to the components of system 10. System 90includes a solar collector assembly 12, water storage tank 14, watersupply and return pipes 20 and 22, including insulated portions 28 and30, pump 26 and differential thermostat 40, as previously described.Control circuit 36 is connected to the differential thermostat 40 and topump 26.

System 90 includes a second differential thermostat 92 connected totemperature sensor 94 located in the return pipe 22 inside of exteriorwall 54 and to temperature sensor 96 located in supply pipe 20 inside ofexterior wall 54. System 90 does not use a flow sensor 38 and does notsense flow using moving parts.

During normal operation of solar heating system 90, pump 26 is actuatedto circulate water through the solar collector 12 and flow the heatedwater back to tank 14, as previously described. Temperature sensor 94detects decreased temperature in pipe 22 due to decreased flow and is anindirect flow sensor. If an ice blockage exists in portion 28 or 30 ofpipe 20 or 22 the blockage will prevent flow of heated water fromcollector assembly 12 to tank 14. The temperature of the water in pipe22 will not rise. When this condition exists the temperature differencebetween the water in pipe 22 will not greatly exceed that in pipe 20, asdetermined by sensors 94 and 96. When this difference is below apredetermined amount, which may be 20° F., differential thermostat 92sends a signal to control circuit 36 to actuate the resistance heatingwires 42 in the exterior portions 28 and 30 of pipes 20 and 22 to meltthe ice blockage, as previously described.

Melting of the blockage and flow of heated water through pipe 22 whichwill raise the temperature of the water in the pipe. When thetemperature of the water in pipe 22 exceeds the temperature of the waterin pipe 20, as again determined by temperature sensors 94 and 96, by thepredetermined amount, the differential thermostat 92 sends a signal tocontrol circuit 36 to deactivate the resistance heating wires in pipeportions 28 and 30. Flow of water through the exterior portions 28 and30 of pipes 20 and 22 melts any remaining ice in the blockage toreestablish normal operation of system 90.

FIG. 7 illustrates third embodiment solar heating system 98 having threeseries connected solar heating assemblies 100, 102 and 104 which replacethe single assembly 12 used in the systems of FIGS. 1 and 6. Theassemblies are each identical to solar collector assembly 12. The threecollector assemblies are connected to water supply pipe 20 and waterreturn pipe 22 of a solar heating system 10 or 98 located inside ofbuilding exterior wall 54. These alternative interior components are notillustrated in FIG. 7.

The outer insulated end 106 of pipe 20 extends from wall 54 to collectorassembly 100 and is connected to the inlet end of water heating pipe 56in assembly 100. Pipe end 106 is surrounded by insulation and a sheath,as previously described. The outlet end of water heating pipe 56 inassembly 100 is connected to an insulated pipe 108 extending fromassembly 100 to assembly 102. Pipe 108 is connected to the inlet end ofpipe 56 in assembly 102. The outlet end of pipe 56 in assembly 102 islikewise connected by insulated pipe 110 to the inlet end of the pipe 56in assembly 104. The outlet end of pipe 56 in assembly 104 is connectedto the insulated outer end 112 of pipe 22 which extends to wall 54. Thecontrol wiring 114 for temperature sensor 46 in assembly 104 extendsthrough wall 54 to the differential thermostat 40 for system 98.Resistance heating wires (not illustrated) extend through outdoor pipesportions 106, 108, 110 and 112 and are connected to power wires 48 and50. The resistance heating wires are actuated to melt ice blockages aspreviously described. Pipes 20, 56, 108, 110 and 22 form a singlepassage water conduit 99 extending from tank 14, through the assemblies100, 102 and 104 and back to the tank.

The system 98 operates essentially like the systems 10 and 90. Pump 26circulates water through the three solar collector assemblies 100, 102and 104 and water is solar heated. The temperature sensor 46 determinesthe temperature of the water in assembly 104, which typically is higherthan the temperatures of the water in assemblies 100 and 102. Thistemperature is used to determine whether the water returned through pipe22 is sufficiently hot to heat the water in tank 14.

FIG. 8 illustrates a fourth embodiment solar heating system 118 whichincludes three parallel connected solar collector assemblies 120, 122and 124. The assemblies are each identical to solar collector assembly12. The three collector assemblies are connected to water supply pipe 20and water return pipe 22 of system 10 or system 98 located insidebuilding exterior wall 54. These components are not illustrated in FIG.8.

Water supply pipe 20 extends outwardly of wall 54 and includes insulatedoutdoor supply branches 126, 128 and 130. The branches are connectedrespectively to the inlet ends of the water heating pipes 56 in thethree assemblies. The outlet ends of the water heating pipes 56 in theassemblies are connected to insulated return branches 132, 134 and 136of return pipe 22. All of the portions of the supply and return pipeslocated outwardly of wall 54 and connected to the three assemblies aresurrounded by insulation and protective sheeting, as previouslydescribed. A single temperature sensor 46 is connected to a waterheating pipe 56 in collector assembly 122. The sensor may be attached tothe water heating pipe in any of the collector assemblies. Insulatedresistance heating wires (not illustrated) are extended through thesupply and return branches of pipes 20 and 22. When an ice blockage issensed, the wires are actuated to melt the blockage, as previouslydescribed. Pipes 20, 56 and 22 form a plural passage water conduit 116extending from tank 14, through assemblies 120, 122 and 124 and back tothe tank.

During operation of system 118, pump 26 flows water from tank 14 throughthe three collector assemblies and flows the heated water directly backto the tank. The system 118 operates like system 10 or 98, as previouslydescribed.

Solar heating systems 98 and 118 use plural solar collector assembliesin order to increase the capacity and performance of the system. The useof a number of small individual solar collector assemblies facilitatesmanufacture, transportation and the mounting of the assemblies on theroof of a dwelling. Frequently smaller assemblies can be mountedadvantageously where it is impossible to mount a large assembly havingthe same heating capacity.

FIGS. 9-11 illustrate a second solar collector 140 which may be used inthe solar collector assemblies 12 of the previously describedembodiments of the disclosure in place of previously described solarcollector 58. Solar collector 140 includes an elongate semi-cylindricalmirror 142, like mirror 62, and a vertical solar absorber 144 located inthe center of the mirror, in the same position as solar absorber 64 ispositioned in mirror 62. Compare FIGS. 2 and 9.

Solar absorber 144 includes two like elongate absorber plates 146 and anelongate, flat water pipe 148 held between the plates. Each plate 146includes elongate strips 150 at the top and bottom of the collector.Strips 150 have uniform thickness. The plates each include anelastically deformable pipe contact energy transfer portion 152extending between the strips 150. Flat recesses 154 on the innersurfaces of portions 152 form a flat pocket 156 extending along theportions 152 between plates 146. Outer surfaces 155 of portions 152 areconcave. The thickness of each energy transfer portion 152 decreasessmoothly from a maximum thickness adjacent strips 150 to a minimumthickness at the centers of the strips. Plates 146 form fromheat-absorbing metal which may be high thermal-conductivity aluminum.Plates 146 are secured together by threaded fasteners passing throughholes 147 and spaced along strips 150. The fasteners may be formed fromstainless steel and are preferably spaced from the aluminum in strips150 by dielectric separators to prevent electrolytic corrosion.

Flat water pipe 148 has opposed wide and normally flat sidewalls 158 andopposed rounded and narrow sidewalls 160. The pipe is fitted in flatpocket 156 with sidewalls 158 abutting the flat pocket 154. Narrow,rounded sidewalls 160 are spaced inwardly from the top and bottom offlat pocket 156.

Water pipe 148 is preferably formed from the same metal as pipe 56,previously described. Likewise, the pipe sidewall may have a thicknessof 0.020 inches to permit outward flexing of the flat sidewalls 158 whenwater in the pipe freezes. The pipe 148 may have a width of three inchesand a spacing between the flat sidewalls of 0.150 inches. The long,closely spaced sidewalls 158 permit elastic outward expansion of thepipe when water freezes.

The pipe may be flattened slightly when the strips 150 are securedtogether in order to assure close surface-to-surface interfaces betweenthe pipe and the plates. Rounded sidewalls 160 may be stressed. Ifdesired, a thin layer of flexible, thermally conductive material may beprovided in the interface between the pipe and the absorber plates, aspreviously described.

During normal operation of solar collector assembly 140, mirror 142reflects solar energy onto absorber 144 and heat is transferred from theabsorber plates 146 to water in pipe 148, as previously described.

In the event that water in pipe 148 freezes and expands, the increasedpressure in the pipe forces the flat sidewalls 158 outwardly and flexesthe portions 152 outwardly as shown in FIG. 11. Maximum deflectionoccurs at the centers of the portions, where the portions 152 arethinnest. Reduced deflection occurs to either side of the centers of theportions. During freezing, the portions 152 and pipe flat sidewalls 158are bowed outwardly within their elastic limits and without permanentdeformation. This means that when water in the pipe melts, the pressurein the pipe decreases and the pipe contact portions and flat pipesidewalls return elastically to their original positions shown in FIG.10. Freezing of water in the pipe does not injure the solar absorber orimpair its efficiency in flowing solar energy to water in the pipe.

What I claim as my invention is:
 1. A solar collector assembly for a hotwater heating system, the solar collector assembly including a solarenergy absorber and a mirror for reflecting solar energy onto the solarenergy absorber; the solar energy absorber comprising an elasticallydeformable metal hot water pipe having a non-circular transverse crosssection with opposed wide and flat sidewalls and opposed short sidewallsjoining the wide and flat sidewalls, and two metal solar energyabsorbing plates, each absorbing plate extending along the length of thepipe and comprising a first elongate solar energy absorbing panellocated to one side of the pipe and having a minimum thickness at thecenter of a pipe wide and flat sidewall and an increasing thickness toeither side of the center of the pipe wide and flat sidewall and anelongate elastically deformable solar energy transfer portion, thetransfer portion in surface-to-surface heat flow physical connectionwith one wide and flat pipe sidewall for transfer of solar energy to thepipe, the solar collecting panel and the solar energy transfer portionof each solar absorber plate including a solar energy absorbing surfacefor receiving solar energy from the mirror, wherein when water in thepipe freezes and expands the pipe wide and flat sidewalls areelastically deformed outwardly and the solar energy transfer portions ofthe solar absorbing plates are elastically deformed outwardly by thelong sidewalls, and when ice in the pipe melts the deformed longsidewalls and the elastically deformed solar energy transfer portions ofthe solar absorbing plates elastically contract and return to theirinitial positions without impairing transfer of solar energy to the pipeor forming leaks in the pipe.
 2. The assembly as in claim 1 wherein eachplate includes a second elongate solar energy absorbing panel having asolar energy absorbing surface, the solar energy transfer portion ofeach plate located between the panels in the plate.
 3. The assembly asin claim 2 including a recess in each plate, the recesses forming apocket between the plates, said pipe in said pocket; and fastenersholding adjacent panels together.
 4. The assembly as in claim 3 whereinsaid plates are formed from aluminum.
 5. The assembly as in claim 4wherein said pipe is formed from austenitic stainless steel.
 6. Theassembly as in claim 5 wherein the axis ratio for the pipe is at least1.50.
 7. The assembly as in claim 5 wherein the wall thickness of thepipe is about 0.02 inches.
 8. The assembly as in claim 3 wherein thepipe wide sidewalls are spaced apart about 0.15 inches.
 9. The assemblyas in claim 8 wherein the pipe has a width of about 3 inches.
 10. Theassembly as in claim 3 wherein the plate short sidewalls are spaced fromthe ends of the pocket.
 11. A solar collector assembly for a hot waterheating system, the solar collector assembly including a solar energyabsorber and a mirror for reflecting solar energy onto the solar energyabsorber; the solar energy absorber comprising a flat and elasticallyexpandable metal hot water pipe having opposed flat and wide sidewallsand opposed short sidewalls joining the wide sidewalls; and two elongatemetal solar energy absorbing plates, each absorbing plate extendingalong the length of the pipe and comprising two spaced solar energyabsorbing panels located to either side of the pipe and an elongateelastically deformable solar energy transfer portion between the panels,each transfer portion having a minimum thickness at the center of thepipe wide sidewall and an increasing thickness to either side of thecenter of the pipe wide sidewall, a flat pocket between the panels atthe energy transfer portions, the pipe in the pocket with the pipe widesidewalls in heat flow surface-to-surface contact with the transferportions for transfer of solar energy from the plates to the pipe, thesolar collecting panels and the solar energy transfer portion of eachsolar absorber plate each including a solar energy absorbing surface forreceiving solar energy from the mirror, wherein when water in the pipefreezes and expands the pipe wide and flat sidewalls are elasticallydeformed outwardly and the solar energy transfer portions of the solarabsorbing plates are elastically deformed outwardly, and when ice in thepipe melts the expanded pipe wide and flat sidewalls and the deformedsolar energy transfer portions of the solar absorbing plates elasticallycontract and return to their initial positions without impairingtransfer of solar energy to the pipe or forming leaks in the pipe. 12.The assembly as in claim 11 wherein said plates are formed fromaluminum.
 13. The assembly as in claim 11 wherein said pipe is formedfrom austenitic stainless steel.
 14. The assembly as in claim 12 whereinthe wall thickness of the pipe is about 0.02 inches.
 15. The assembly asin claim 11 wherein the pipe has an axis ratio of 1.50 or greater. 16.The assembly as in claim 11 including thermal conductive materialbetween each long pipe sidewall and the adjacent transfer portion.
 17. Asolar collector assembly for a hot water heating system, the solarcollector assembly including a solar energy absorber and a mirror forreflecting solar energy onto the solar energy absorber; the solar energyabsorber comprising an elastically deformable metal hot water pipehaving a non-circular transverse cross section with opposed widesidewalls and opposed short sidewalls joining the wide sidewalls, andtwo metal solar energy absorbing plates, each absorbing plate extendingalong the length of the pipe and comprising a first elongate solarenergy absorbing panel located to one side of the pipe and having aminimum thickness at the center of a pipe wide sidewall and anincreasing thickness to either side of the center of the pipe widesidewall and an elongate elastically deformable solar energy transferportion, the transfer portion in surface-to-surface heat flow physicalconnection with one long pipe sidewall for transfer of solar energy tothe pipe, the solar collecting panel and the solar energy transferportion of each solar absorber plate including a solar energy absorbingsurface for receiving solar energy from the mirror, wherein when waterin the pipe freezes and expands the pipe wide sidewalls are elasticallydeformed outwardly and the solar energy transfer portions of the solarabsorbing plates are elastically deformed outwardly by the widesidewalls, and when ice in the pipe melts the deformed long sidewallsand the elastically deformed solar energy transfer portions of the solarabsorbing plates elastically contract and return to their initialpositions without impairing transfer of solar energy to the pipe orforming leaks in the pipe.